DAVID Cameron will today promise to keep the “triple lock” guarantee on pensions for the life of the next Parliament if the Tories win next year’s general election.

The pledge ensures state pensions rise each year in line with either wages, prices or by 2.5 per cent, whichever is highest.

The announcement reveals the issue is likely to become a key battleground between the Tories and Labour. While the Tories have excluded the state pension from their welfare spending cap, Labour has confirmed it plans to include the pension in its review of welfare costs.

The Prime Minister revealed the flagship commitment in a series of interviews today. He said: “I am determined to give people who have worked hard and done the right thing during their working lives real security and peace of mind in retirement.”

The triple lock has already helped to protect pensioners’ incomes at a time when earnings growth has been low.

As a result, the basic state pension will be about £440 a year higher from April than it would have been if it had risen in line with average earnings since 2011. The pledge will be paid for by a new cap on other welfare spending and bringing forward the increase in state pension age to 66 and 67.

While it will prove popular with retirees, a poll today indicates the Tories need to attract far wider support to stand any chance of winning outright in 2015.

The poll for Tory website Conservative Home shows 37 per cent of those who backed the party in 2010 would not do so now.